A low cost intravenous injection system can include a peristaltic pump which pumps a quantity of intravenous fluid in pulses, such as every time a tube is compressed. The fluid pulses are applied to a pressure moderator which smooths the pressure, and is applied from the pressure moderator to a needle or the like that is connected to a patient's vein. A system of this type is described in U.S. Pat. No. 4,345,594 by Bisera et al. Two types of problems that can arise in intravenous injection, are infiltration and occlusion. In infiltration, fluid passes out of the needle with very low resistance. This can occur when the tip of the needle has withdrawn from the vein and is pumping fluid into an area surrounding the vein where it does not experience the moderate backpressure that would be normally encountered in a vein. In occlusion, there is greater than expected resistance to the outflow of fluid from the needle, as where the tip of the needle is blocked by tissue. A simple system for monitoring the injection system to guard against infiltration or occlusion, would add to the usefulness of simple injection systems.